1. Field of the Invention
This invention relates generally to downhole gas generators, and more particularly to a method for cooling a downhole gas generator using a plurality of independently controlled cooling jackets.
2. Description of Related Art
The following art defines the present state of this field:
Tilmont et al., U.S. Pat. No. 8,387,692, teaches a downhole steam generation apparatus that includes an injection section, a combustion section, and an evaporation section. The injection section may include a housing, injector elements, and injector plate.
Ryan et al., U.S. Pat. No. 4,558,743, teaches a steam generator for producing steam in a well casing for injection into a borehole for use in secondary and tertiary recovery of hydrocarbons. Fuel is injected axially into a combustion chamber having a reduced orifice in the bottom thereof and oxygen is introduced tangentially from a plurality of ports in the top of the combustion chamber to create a stable vortex flame. A portion of the walls of the combustion chamber are formed from a porous, sintered stainless steel cylinder through which water is pumped to cool the walls of the chamber and to form steam. The combustion products are mixed with a water mist in a steam generating section to form steam.
Fox, U.S. Pat. No. 4,385,661, teaches an apparatus for generation of steam in a borehole. The system includes a feedback preheater for the fuel and water before entering the combustor assembly. First, combustion gases are conducted from the combustion chamber to locations in proximity to the water and fuel supplies. Secondly, both hot combustion gases and steam are conducted from the borehole back to the water and fuel supply. The water used for conversion to steam is passed in a countercurrent manner through a plurality of annular water flow channels surrounding the combustion chamber. In this manner, the water is preheated, and the combustion chamber is cooled simultaneously, thereby minimizing thermal stresses and deterioration of the walls of the combustion chamber. The water is injected through slotted inlets along the combustion chamber wall to provide an unstable boundary layer and stripping of the water from the wall for efficient steam generation. Pressure responsive doors are provided at the steam outlet of the combustor assembly. The module is positioned in the water flow channel to maintain a relatively constant, controlled temperature.
Griffin et al., U.S. 20040069245, teaches a steam generator for reacting a stoichiometric mixture of hydrogen and oxygen, and injecting water into the hot reaction gases. The generator includes a pilot ignition chamber, a combustion and evaporation chamber with reaction zone, an evaporation zone and outlet nozzle, and a catalytic afterburning chamber. The figure also illustrates the feed devices for supplying a fuel, an oxidizing agent and water.
Couto, U.S. 20110000666, teaches a gas generator which generates a vitiated steam, which is a mix of water steam with combustion gases. The device of this invention may also be attached in petroleum wells, making feasible the extraction of petroleum from the mature wells. The device includes a vaporization chamber attached to the combustion chamber of a rocket engine, said combustion chamber is externally involved by a cooling system, and the nozzle includes spray water injectors.
Other references included as a matter of general interest include the following: Tilmont, et al., U.S. 2011/0127036; Retallick, et al., U.S. 2008/0053655; Kraus et al., U.S. 2006/0000427; and Person, U.S. 1993/5,259,341. The above-described references are hereby incorporated by reference in full.
The prior art teaches various forms of downhole gas generators. The prior art systems struggle, however, to cope with the significant heat of combustion, particularly in the confined space of the borehole. The prior art does not teach a plurality of independently controlled cooling jacket segments around a combustion chamber housing, with each annular cooling jacket segment being individually controlled so that an optimum mass of water flows into and out of the segment, thereby preventing the formation of hot spots in the combustion chamber housing. The present invention fulfills these needs and provides further advantages as described in the following summary.